docs: def value(self):
          '''Return single value or list of values from the attribute.
             If FORCE_ATTRIBUTE_VALUE_AS_LIST is True, always return a
             list with values.
          '''
          if len(self.__dict__['values']) == 1 and current_app.config['FORCE_ATTRIBUTE_VALUE_AS_LIST'] is False:
              return self.__dict__['values'][0]
          else:
              return self.__dict__['values']